This invention relates to electrical terminations and connectors used in power and information transmission systems. More specifically, the invention provides electrical terminations and connectors for substantially rigid cable and which hermetically seal the conductors therein from adverse environments.
In applications where electrical equipment operates in adverse environments, it is important to protect the cable and the connectors which supply electrical energy and which communicate control signals with the equipment. It is not uncommon for the cable to be a multi-leg rigid cable having an armor jacket with each individual conductor therein insulated and protected by a further sheath. The jacket and the sheath can include a steel or other metal structure. The cable legs connect to the equipment or to other cables through connectors or by field splicing.
Typical adverse environments occur, for example, in the reactor vessel of a nuclear reactor, in a deep underwater environment, and in an oil well. In these and like situations, it may be necessary that an electrical connector or an electrical penetrator through a pressure barrier transmits electrical power and/or control signals across the barrier and maintains an environmental separation between the different conditions on opposite sides of the barrier. The electrical cables, connectors and penetrators typically are subjected to temperatures and pressures that can vary over wide ranges. They can also be subjected to corrosive liquids and gases.
In addition, it can be extremely costly and time consuming to repair these components in the event of a failure. For example, the repair of an electrical failure in a deep oil well typically requires the costly removal of equipment from the well and the subsequent replacement; all with the further cost of having the well shut down and hence non-productive. Such a system shut down and the repair procedure can endanger both personnel and the environment.
As the oil reservoir in a production oil field becomes depleted, the reservoir loses positive pressure and the oil flow diminishes, yet there may still be substantial amounts of oil in the reservoir. In addition, some oil fields and wells on the periphery of oil fields do not initially have positive pressure. Consequently, in these situations, pumping techniques are employed to recover oil from the well.
This pumping is accomplished by placing an electric submersible pump (ESP) into the pipe-like casing of the oil well and by providing various pressure barriers or bulkheads, also termed "packers", to seal the pressure between sections of the casing. Typically, power is delivered to the pump, which may be as deep as 15,000 feet below sea level, by a multi-conductor ESP power cable. In one mode of installation, the pump is located below a packer, and a motor lead extension (MLE) cable extends upward in the well casing from the motor of the pump to that packer, where it connects to the power cable. The packer has an electric penetrator structure breeding electrical connections between the two different pressure environments that the packer separates. In another mode of installation, the submersible pump is housed in a production shroud located just above a packer. The electric penetrator structure penetrates the shroud and is connected to the ESP power cable and to the MLE power cable in a similar manner. Typically, each conductor of the ESP power cable is connected to a corresponding conductor of the motor lead extension cable by means of a packer penetrator. The packer penetrator typically has an American Petroleum Institute (API) standard fitting or API adapter to attach to the packer either on the uphole or the downhole side.
A typical prior MLE cable installation has an armored three-conductor cable and illustratively is one hundred or more feet long. Each cable leg includes a number 2, 4 or 6 AWG (American Wire Gage) solid copper conductor core which is insulated. The several insulated conductor cores are covered with a further insulating layer and with an outer protective sheath or jacket that is of lead or nitrile rubber. To form the connection between the ESP power cable and the motor lead extension cable, the armor and the lead protective layer and the insulating layers are removed to expose the conductors. Each conductor of the power cable is connected to a corresponding conductor of the MLE cable, either directly or by way of a conductor in an intermediate-pressure boundary header. The exposed conductors are overmolded with a rubber insulating layer and covered with a steel shell having an API adapter.
The environment in an oil well below the bottommost or deepset packer is extremely aggressive. The pump, the motor lead extension and the packer penetrator structure can be exposed to corrosive materials mixed with sand and gravel at high temperatures and pressures. Unfortunately, the reliability of the theregoing and other conventional MLE power interconnect structures tends to be poor. A normal expected life of the prior structures often does not exceed 150 to 200 days. Due to the excessive costs associated with removing the submersible pump, as well as the cost of down time, it is desirable for the system to have a longer service life.
A common failure in a deep oil well is electrical shorting between the conductors or electrical shorting between a conductor and ground. Some of these failures occur as a result of the degradation of electrical insulation, often due to the migration of gas and fluids into the packer penetrator, in combination with the high temperatures and pressures to which it is exposed. Other failures occur as result of mechanical stresses produced by cycles of differential expansion, e.g. thermal expansion and contraction. These stresses are sufficient, for example, to extrude insulation through a seemingly minute opening, especially under high temperature conditions. Upon cooling, the insulation contracts and the extruded material leaves a void in an insulating layer. This void can quickly become filled with corrosive environmental elements that further degrade the insulating layer. Repeated cycles of heating and cooling can thereby progressively deteriorate the insulating structure until an electrical short circuit occurs, typically between a cable conductor and the grounded sheath. That condition can cause a complete system failure.
Other failures occur when hard-wired and/or relatively stiff cables are flexed or otherwise subjected, as during installation, to localized mechanical stresses. These stresses can lead to physical degradation of the cable and of the penetrator. Furthermore, a protective jacket of lead can be penetrated by gas or other fluids, which in turn degrade the insulating layer underneath.
It is an accordingly object of this invention to provide electrical cable, termination, connector and penetrator structures that operate reliably for extended time periods in adverse and cyclic pressure and/or temperature environments.
Another object is to provide electrical terminations for rigid cable and which are capable of extended operation under adverse and cyclic environments.
It is also an object of the invention to provide electrical terminations for rigid cable and which are hermetically sealed to resist degradation by an aggressive adverse environment.
A further object of the invention is to provide the foregoing electrical structures suited for deployment in inaccessible locations, such as within a deep well casing.
Other objects of the invention will in part be obvious and will in part appear hereinafter.